1. Field of the Invention
This invention relates to well packers of the type used for sealing a cylindrical member to a circumscribing conduit in a well bore such as, for example, sealing a tubing string to a surrounding casing or well liner.
2. Description of the Prior Art
Well packers are known for selectively sealing and/or anchoring a tubing string to a surrounding well conduit or liner. Such devices are known which can be set in the sealing/anchoring configuration by manipulation of a tubing string from which the packer is suspended, or by application of hydraulic pressure by means of the tubing string. Such devices are also known which can be released from the set configuration and retrieved from the well by appropriate manipulation of the tubing string.
In many applications, the well packer assembly includes gripping and sealing elements which are located concentrically about a single cylindrical tubing member. The gripping and sealing elements are movable radially between relaxed and extended positions for gripping and sealing a surrounding conduit. Dual string packers are also known in which a pair of tubular mandrels extend through the body of the packer with the gripping and sealing elements circumscribing both of the tubular mandrels. Dual string well packers are also known which feature a sealing element located on either side of the gripping elements to form a "twin seal" arrangement.
In setting the twin seal, dual string packer, it is desirable to eliminate the need for mandrel movement. Particularly in the case of a production packer, where each of the dual tubing strings may extend for great lengths, it is important that the packer be set in sealing engagement with the surrounding well conduit without causing relative movement between the tubing strings. It is also important in a twin seal packer of the type described that the upper seal element be compressed and the gripping elements engaged before the lower seal element is compressed. By locking the setting force of the packer into the upper seal element before compressing the lower seal element, the lower seal does not "drag" on the surrounding well conduit, and the tubing strings below the packer are not placed in compression.
These and other objects will be accomplished by the improved twin seal, dual string packer which is described in the specification which follows.